Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 60: [MA] Joint Session "Surface Magnetism II" (jointly with O)

O 60.12: Talk

Thursday, March 29, 2012, 12:30–12:45, EB 301

Spin-transfer torque switching efficiency in SP-STM experiments — •Andreas Sonntag, Stefan Krause, Gabriela Herzog, Anika Schlenhoff, and Roland Wiesendanger — Institute of Applied Physics, University of Hamburg, Germany

The tunnel current generated in spin-polarized scanning tunneling microscopy (SP-STM) experiments can be used to manipulate the switching behavior of superparamagnets [1] or even to reverse the quasistable magnetization of nano-islands [2]. Two main contributions involved in magnetization switching could be identified: Joule heating and the spin-transfer torque.

In our study we investigate the influence of a spin-polarized tunneling current on the switching behavior of superparamagnetic Fe nano-islands on the W(110) surface. Analyzing the lifetimes of the two magnetic states in dependence of the current, Joule heating and spin-torque effects are separated and quantified [3]. While the Joule heating decreases both lifetimes equally, the spin-torque lifts their degeneracy. Both effects are found to scale linearly with the tunneling current. By introducing the so-called spin-transfer torque viscosity and normalizing the torkance with respect to the magnetic moment of the free layer, we compare our findings to experiments performed on lithographically fabricated magneto-tunnel junctions. The results show a comparatively high spin-transfer torque efficiency in our experiments.

[1] S. Krause et al., Science 317, 1537 (2007).

[2] G. Herzog et al., Appl. Phys. Lett. 96, 102505 (2010).

[3] S. Krause et al., Phys. Rev. Lett. 107, 186601 (2011).